1. Field of the Invention
The present invention relates to a method of embedding at least one optical fiber in a multilayer printed circuit board without causing chemical or thermal damage to the optical fiber, whereby high frequency signals are capable of being transmitted without noise.
2. Description of the Prior Art
As well known to those skilled in the art, when electronic components are electrically connected with each other, or power voltage or ground voltage is supplied in large-scaled devices such as a computer, an electric signal is conventionally processed by a patterned conductive copper layer laminated on a printed circuit board where at least one electric circuit is formed on an inner and outer layer. Meanwhile, nowadays, there is a need for a broad bandwidth and a high-speed signal processing in order to cope with an increased data traffic and transmission according to a rapid increase of use of the Internet and improved service on the Internet. However, the electric signal is subject to a restriction attributable to electro magnetic susceptibility (EMS) during a high speed switching within a giga band, and thus a medium capable of replacing a method of patterning a copper plate is inevitably required.
To avoid the above-mentioned disadvantage, a method of applying an optical fiber to a printed circuit board is suggested, in which both an electric signal and an optical signal are propagated on a single substrate in such a way that an ultra high-speed data communication is interfaced with the, optical signal, a data storage and a signal processing in the components are conducted with the electric signal and a signal transmission is conducted by an optical signal.
As for a first and a second generation back plane, a signal processing is conducted with respect to the optical fiber in the so-called “point to point” manner. But, many studies have been performed on an optical signal interface using a multi-channel manner so as to simultaneously process a large amount of data since a third generation.
For example, U.S. Pat. No. 6,005,991 discloses a printed circuit board assembly comprising a printed circuit board having an interior portion and an edge portion surrounding the interior portion, and a flexible optical circuit disposed upon the interior portion of the printed circuit board. According to this patent, the flexible optical circuit comprises a pair of at least partially flexible sheets and a plurality of optical fibers extending between respective first and second ends, the plurality of optical fibers disposed between the at least partially flexible sheets. In addition, a multi-fiber connector is mounted on the respective first ends of the plurality of optical fibers. However, this patent is disadvantageous in that the flexible sheet is made of a specific film such as MYLAR® or KAPTON® film, not a common material for the printed circuit board, thus incurring a high cost for materials. Furthermore, this patent discloses a method of mounting the flexible sheet having the optical fiber embedded therein on the printed circuit board, but does not teach or suggest a method of embedding the optical fiber in an interior layer of the printed circuit board.
In addition, U.S. Pat. No. 6,370,292 proposes an optoelectronic, multilayer printed circuit board comprising at least one outer layer to be fitted with a plurality of components, an electrical printed circuit trace on the exterior of the outer layer, a layer system including a plurality of additional, optically transparent layers and arranged with respect to the at least one outer layer, and at least one optical signal-transmission paths patterned in an arbitrary layout and cross-section in the layer system as an integrated multimode strip waveguide. However, this patent does not teach or suggest any specific and efficient way for embedding the optical fiber in an inner layer of the printed circuit board without chemical or thermal damage to the optical fiber.
Therefore, there remains a need to develop a technology of embedding the optical fiber in a multilayer printed circuit board using a conventional substrate without causing chemical or thermal damage to the optical fiber.
The present inventors have conducted extensive studies to solve the above problems, resulting in the finding that an optical fiber can be embedded in a multilayer printed circuit board without causing chemical or thermal damage to the optical fiber by forming a groove for receiving the optical fiber in a dielectric substrate layer by a router bit process, followed by laminating at least one optical substrate having the optical fiber embedded in the groove using an adhesive liquid (such as an epoxy-based adhesive liquid) with at least one printed circuit board, thereby accomplishing the present invention.